1. Field of the Invention
This invention relates, in general, to the construction of water craft and, in particular, to a new and useful water craft having a cavity opening to the sea which is connected through a conduit in the hull through an opening below sea level immediately adjacent the opening to the sea of the cavity.
2. DESCRIPTION OF THE PRIOR ART
The present invention has particular application in respect to the construction of ships having cross flow channels or steering channels which are subject to flow disturbances during operation and to methods of improving such flow characteristics. The invention also relates to cavities in the outer skin of the water craft, such as sea chests or sea boxes as well as the cross flow channels for the cross jet steering gear. Sea boxes or sea chests communicate with suction conduits of a cooling water and ballast pumps while in the cross channel, there are provided rotatable devices, such as propellers which produce a thrust for maneuvering the ship. Cross jet rudders are started, particularly during a low or middle speed motion of the ship when the effect of the main rudder is reduced.
Even at low speeds of the ship, flow conditions are produced in the cavities which have sea openings below water level which are undesirable and which interfere with the operation of the ship to the extent that they cause increased power consumption. Thus, for example, whirls which are created in sea boxes impair the delivery of the cooling and ballast water pumps and similar flow conditions in cross flow channels of jet rudders affect not only the thrust and the power consumption of the cross jet rudders but also the ship's resistance. Due to these flow conditions, the propeller of a cross jet rudder is exposed to the inflow in a non-symmetrical manner and vibrations wear and decreasing thrust with a frequently increasing power consumption are observable, even at low speeds of the ship. The dimunition of the transverse force of a cross jet rudder is due to over- and under-pressure fields which are induced at the outer skin in the vicinity of the deviated jet during the motion of the ship. In order to abate these parasite pressure and suction fields, the concept of pressure equalizing channels has been conceived and successfully introduced into the practice. In order to improve the conditions at the inlet side of the cross jet steering gear, rounds or collar-like shapes of the transition surface in the outer skin of the ship have been provided also.
It has been proved that during a forward motion of the ship, a cross jet rudder can be overloaded, while during a backward motion, as a rule, the power consumption decreases with increasing speed of the ship (BRIX, J.: Model tests with the SCHOTTEL cross jet gear S 500 L, HANSA-STG-Heft 1971; BRIX, J.: Cross jet rudder with pressure equalizing channels A-S-T, HANSA, 18/1972).
Considerable problems arise in the delivery of cooling or ballast water from conventional sea boxes during the travel of a ship. Such problems assumes dangerous proportions at increased speeds of the ship and thereby higher mechanical power outputs result in view of the volume of cooling water which is required. It is very essential that the performance of cross jet rudders be improved particularly for their operation during as ship's travel in estuaries, channels and harbor basis and during travel in fog or in off-shore service where the effectiveness of the main steering device is relatively small.